One of the top celebrity profilers at Vanity Fair, writer Jennet Conant, quit the magazine after Editor-in-Chief Graydon Carter spiked a story on Brill’s Content Editor Steve Brill that was slated to run in the July issue.

Conant said the piece was on target to run in the July issue that was being put to bed this week and she was stunned to hear it was being pulled.

“you could have knocked me over with a feather,” she said. As recently as Monday, she said she was inserting a new anecdote into the story from Rolling Stone founder Jann Wenner.

Back on April 1 when she handed in the manuscript, she said she got a fax from Carter calling it a “great piece…Are we being too tough on him? Oh, hell, – no we’re not,” said the fax, which she supplied to The Post.

The first hint that it was being canned from the July issue came at the P.E.N. literary awards on Wednesday night in Manhattan, Conant said. She said she heard that Brill was telling people the story was being killed.

Brill no insists he never said that. “The last thing I heard was that it was in the July issue,” said Brill, who said his only contact with Carter in recent months was a brief encounter at a Michael Ovitz cocktail party earlier this year.

Brill said he had refused to be interviewed for the piece because he had heard it was to be a hatchet job.

Carter said only that he had pulled the story from the July issue because “I just said it was not at a stage that I wanted to publish it.”

Yesterday, in a showdown with Carter, Conant made good on an earlier threat to quit, but says she is still mystified by the change of heart by Carter.

“It was still full throttle on Monday. The story was in production,” she says.

“She resigned,” said Carter. “I thought it was a foolish thing and a rash thing, but it was her call.”

Things were once a lot rosier between Conant and Carter.

Conant had penned the controversial piece in the September 1997 issue of Vanity Fair in which she claimed that a City Hall Deep Throat had told her that Mayor Giuliani was having an affair with Christyne Lategano, the mayor’s director of communications.

Some portions of the story came under fire but Conant never backed down from its main thrust and Carter backed her to the hilt at the time.

More recently, however, Carter has been less enamored and has spiked two of the three major stories she has worked on for the magazine in the past 18 months. Only a Barbara Walters profile made it into the magazine, while the Brill piece and an earlier piece on TV writers were spiked.